Polymerization of n-vinyl pyrrole compounds



Patented Mar. 27, 1951 UNITED STATES PATENT OFFICE POLYMERIZATION OFN-VINYL PYRROLE COMPOUNDS No Drawing. Application December 20, 1944,

\ Serial N0. 569,101

6 Claims. (01. 260-88.3)

The present invention relates to an improved method of polymerizingN-vinyl compounds, such as N-vinyl pyrrole, or N-vinyl compoundscontaining the pyrrole ring, such as N-vinyl carbazole, N-vinyltetrahydrocarbazole, N-vinyl propyl carbazole, N-vinyl indole, andN-vinyl naphthocarbazole which may be produced in the manner disclosedin United States Patent No. 2,066,160 to Reppe et al., and may bepolymerized in order to produce polymeric N-vinyl compounds.

When these N-vinyl compounds are polymerized, polymeric N-vinylcompounds are obtained which possess many unique and valuableproperties. Polymeric N-vinyl compounds, such as polyvinyl carbazole,have been produced which are particularly valuable for use in theelectrical field since the polymers which possess high mel*- ing orsoftening points also have very valuable electrical properties and arethus quite valuable as low loss electrical insulation materials incapacitors and elsewhere. Such polymeric N- vinyl compounds and methodsof producing the same are disclosed in United States Patent No.2,072,465 to Reppe, Keyssner and Dorrer.

Ihe present invention is particularly directed to improvements in themethod of polymerizing N-vinyl compounds in which the monomeric N- vinylcompound is dissolved in a solvent and polymerization is effected by theaction of an acid catalyst.

I have discovered that the solvent employed during the polymerizationexerts a marked efiect on the polymerization reaction and on theproperties of the polymers produced.

It is, therefore, an object of the present invention to provide animproved process for polymerizing N-vinyl compounds in which thesolvents employed for the polymerization are such that desirable typesof polymers may readily be obtained in very good yields. Other andfurther objects will be apparent as the present description progresses.

In practicing the present invention, the mono-. meric N-vinyl compoundis dissolved in a halogenated aromatic solvent in which at least one ofthe carbon atoms in the ring is halogenated. Suitable solvents aremono-, chloro-, bromoand fiucro-oenzene and orthoor meta-dibromo-, dchloroand difiuoro-benzene. The particular ratio of solvent to monomerwhich is employed per se exerts relatively little influence on theoperability of the process and the exact proportions to be employedwill, in general, be deter mined by practical and economicconsiderations,

taking into account the other conditions, such as the temperatureemployed during the polymerization, and the type of polymer desired as aproduct.

In practicing the present invention, a sufficient amount of solventshould be employed to give a fluid, readily handable solution which isnot too viscous after polymerization. In order to obtain a solution ofthis type at room temperature, a

ratio of solvent to monomer of at least 1:1 is generally desirablesince, at higher concentrations of the monomer, the solution, afterpolymerization, is apt to be too viscous to be easily handled. Slightlyhigher ratios of solvent to monomer are generally preferred since whenmore solvent is present, the heat generated during polymerization isdissipated better and more easily than when a low ratio of solvent tomonomer is employed. As a practical matter, solvent to monomer ratios ofapproximately 2:1 or 3:1 may be used to good advantage, since, at thisratio of dilution, the product obtained is quite fluid and can behandled readily and, at the same time, the heat generated onpolymerization may be removed without unusual difficulties, while theamount of solvent which must be recovered following poiyrnerization isnot excessive. Solvent to monomer ratios greater than approximately 10:1are, in general, undesirable since the separation of the solvent rom thepolymer, after polymerization, and the recovery of the solvent when suchrelatively dilute solutions are employed becomes unnecessarilyexpensive.

The temperature of the solution is then adjustez. to that at which it isdesired to carry out 'ihe polymerization. When the other conditions ofthe reaction remain unchanged, the nature of the polymerization productobtained is influenced primarily by the temperature at which thepolymerization is conducted, the degree of polymerization of theresultin polymer varying inversely as the temperature. The exacttemperature to be employed will, therefore, largely be deter- Iflifld bythe type of polymer which is desired. It should be noted, however, thatwith the solvents oi the present invention, it is possible to obtain ahigher degree of polymerization at a given temperature, as indicated byviscosity measurements of the polymer, than is possible when thesolvents suggested in the prior art are employed. Useful polymers havebeen produced in accordance with the process of the present invention astemperatures varying from '75 C. to temperatures as high as +50 C.,although in general, the polymerization will not be conducted attemperatures much above room temperature.

Those skilled in the art can readily select, by simple preliminary test,the preferred temperature at which to conduct the polymerization,bearing in mind the nature of the polymer which is desired and the otherconditions of reaction, such as the catalyst, which are to be employed.

The particular solvent which is employed will be determined primarily byeconomic considera tions and the temperature at which the polymerizationis to be effected. Mixtures of 2 or more of the solvents employed in thepresent invention may advantageously be employed when operating atrelatively low temperatures in order to obtain a solvent having a lowermelting point than certain of the specific solvents employed in thisinvention.

Ghee the solution of the monomer and the solvent has been adjusted tothe desired temperature, the polymerization may readily be effected byadding an acid catalyst to the solution. The catalyst is preferablyadded relatively slowly and with constant stirring so as to avoid tooviolent a reaction and consequent undesired rise intern perature. Wehave found that any acid catalyst, particularly those of the typeclassified as Friedel-Crafts reaction catalysts, are effective for thepurposes of the present invention. Practically all inorganic acids, suchas sulfuric or hydrochloric acids, are effective, as well as manyorganic acids, such as acetic acid. In addition, the salts of strongacids with weak bases, such as aluminum or zinc chloride, are quiteeffective. Our preferred catalyst is borontrifluoride and the subsequentdescription of the present invention will be limited to the use of thismaterial as a catalyst. However, it should be understood that other acidcatalysts may also be employed. Ehe amount of catalyst which it isnecessary to employ may be varied Within relatively wide limits. Asuflicient amount of catalyst must be employed to effect completepolymerization. However, in general, the best polymers are obtained whenthe use of any noticeable excess of catalyst is avoided. Too greatanamount of catalyst tends to produce readily infusible and insolublepolymers which are desirable only for limited applications. Theirformation, which is indicated by gelling ofthe reaction mass, shouldtherefore be avoided. It is also preferable to avoid the formation ofthe soluble and lower melting type of polymers.

hose skilled in the art can readily determine, by simple test, thespecific amount of catalyst which is necessary to effect completepolymerization.

On addition of the catalyst, the polymeriza tion proceeds rapidly and arise in temperature ofv the solution can be detected. It is generallydesirable, therefore, to cool the reaction mass in order to control thetemperature of reaction and prevent any rise in temperature above thatat which it is desired to carry out the reaction. After the desiredamount of catalyst has been added, agitation of the mixture is continueduntil polymerization is completed.

When the polymerization has been completed, as indicated by no furthergeneration heat, the catalyst s preferably inactivated in any cesiredmanner, for instance, by the addition of water or of a small amount ofalkali, such as an alkali metal hydroxide or ammonia. The poly mer maythen readily be separated from the solvent by distillation of thesolvent or by precipitation on addition of a second liquid, whichdissolves the solvent employed for the polymerizapolymer was vacuumdried.

tion but which is not soluble in and does not dissolve the polymer.Methanol or acetone are satisfactory precipitants for the polymer, sincethey are completely soluble in the solvents employed for polymerizationbut do not dissolve t -e polymer. Other separation steps or combinationsof various separation steps, such as partial distillation of the solventemployed for the poly- 11161122361011, followed by precipitation of thepolymer by addition of methanol, may be employed.

The following specific examples illustrate the present invention, theparts are by weight:

Example 1 One hundred parts of N-vinyl carbazole were dissolved in 300parts of chlorobenzene by stirring in a reaction vessel, care beingtaken to ex clude atmospheric oxygen and moisture. The solutionwaschilled to 5 0., and a minor amount of BFaZl-lzOKas a 1% solution indioxane) was added gradually and with constant stirring and cooling soas to avoid an increase in temperature. Upon completion of catalystaddition, the temperature was allowed to rise to approximately 0 C. Atthe end of the reaction period, the original solution was a viscoussyrup. Further catalytic action was arrested by the addition of 10 partsof water. The chlcrobenzene was then removed by steam distillation,while agitation was continued, and finally the residual The polymeric N-v'inyl carbazole prepared in this way had a characteristic viscosity of50 and was suitable for the fabrication of compression or extrusionmolded articles.

Under similar conditions, the use of toluene as a solvent gave a polymerof much lower molecu- Example 2 A solution of parts of N-vinyl carbazolein 159 parts of o-dichlorobenzene was treated with a minor amount of a3% solution of BFs. dibutyl ether in dibutyl ether, added slowly andwith oonstantstirring. After a polymerization period of 18 hours, duringwhich the temperature was controlled at 15 C., the original solutionbecame highly viscous. The polymer was precipitated by the addition ofmethanol. After filtration, a second treatment with boiling methanol wasemployed to effect further purification. After dry ing, 89 parts of awhite, fiocculent polyvinyl carbazole suitable for molding, paperimpregnation, and metal coating were recovered.

Under similar conditions, a much poorer grade of polymer is obtainedwhen benzene is employed as the solvent.

Example 3 electrical insulation purposes.

The polymer prepared in ligroin, toluene, xylene and their mixtures,with the same catalyst and other conditions the same, is not at allsuitable for the above uses. It has a lower melting point, is morebrittle, etc.

Example 4 A reaction vessel, provided with a means of' stirring andcooling, was charged with 50 parts of N-vinyl carbazole and 100 parts ofchlorobenzene, care being taken to exclude atmospheric moisture. Afterchilling to 3 C., there was added slowly, with vigorous agitation, 2parts of a 1% solution of SnCl-r in dibutyl ether and 0.25 part of a 1%solution of BF3.2H2O in dioxane. The temperature rose from 3 C. to C.but the poly merization did not get out of control and proceededsmoothly. At the end of 20 hours, the re action mass was very viscous.The polymer was precipitated by the addition of methanol. After drying,there resulted 45 parts of polymeric N- vinyl carbazole which softenedat about 250 C.

Under similar conditions, the reaction was difiicult to control, whentoluene was used as the solvent, and a much lower quality productresulted.

Example 5 A solution of 100 parts of N-vinyl carbazole in 100 parts ofo-dichlorobenzene and 100 parts of chlorobenzene was placed in areactor, provided with an efficient stirrer, and chilled to -30 C. aftersolution. Upon adding a small amount of a 3% solution of BF3. dibutylether in dibutyl ether, with rapid stirring, the temperature rose from-30 C. to C. After 18 hours at 25 C., the resulting viscous solution wastreated with an excess of methanol and the polymer precipi tated out inlong, fibrous threads. This material was excellent for preparingcompression molded articles.

Example 6' Twenty-five parts of vinyl carbazole were dissolved in amixture of 25 parts of bromobenzene, 25 parts of fluorobenzene and 25parts of chlorobenzene. The solution was cooled to '70 C. and a minoramount of BF's. diethyl ether (as an 0.1 solution in methylene chloride)was added with stirring. Polymerization set in immediately The resultingpolymer was very suitable for the production of unsupported films.

I claim:

1. In a process of polymerizing N-vinyl pyrrole compounds wherein anN-vinyl pyrrole compound dissolved in a liquid solvent is subjected tothe action of an acid polymerization catalyst, the improvement whichcomprises dissolving said N- vinyl pyrrole compound in a solventselected from the class consisting of monochlcro monobromo, andmonofiuoro-benzene and ortho and meta-dichloro-, dibromoanddifluoro-benzene and subjecting the thus-obtained solution, while liquidand at a temperature below 20 C., to the action of an acidpolymerizationcatalyst in such a predetermined minor amount as issuificient to effect complete polymerization said N-Vinyl pyrrolecompound, but which is less than that at which insoluble material isformed in the reac tion mass.

2. In a process of polymerizingN-vinyl carbazole wherein N-vinylcarbazole dissolved in a liquid solvent is subjected to the action of anacid polymerization catalyst, the improvement which comprises dissolvingsaid N-vinyl carbazole in a solvent selected from the class consistingof monochloro-, monobromoand monofiuoro-benzene and orthoandmeta-dichloro-, dibrorneand difiuoro-benzene and subjecting the thusobtained solution, while liquid and at a tempera ture below 20 C., tothe action of an acid polymerization catalyst in such a predeterminedminor amount as is sufficient to effect complete polymerization of saidN-vinyl carbazole, but which is less than that at which insolublematerial is formed in the reaction mass.

3. The process as defined in claim 2 wherein the acid polymerizationcatalyst specified is boron trifluoride.

4. The process as defined in claim 3 wherein the solvent specified isortho dichloro-benzene.

5. The process as defined in claim 2 wherein the acid polymerizationcatalyst specified is tin tetrachloride.

6. The process as defined in claim 2 wherein theacid polymerizationcatalyst specified is a mixture of boron trifluoride and tintetrachloride, and the solvent specified is chlorobenzene.

WERNER FREUDENBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,072,465 Reppe et a1 Mar. 2,193'? 2,087,079 Wolii July 13, 1937 2,231,905 Hanford et al Feb. 18,1941 FOREIGN PATENTS Number Country Date 500,211 Great Britain Feb. 6,1939

1. IN A PROCESS OF POLYMERIZING N-VINYL PYRROLE COMPOUNDS WHEREIN ANN-VINYL PYRROLE COMPOUND DISSOLVED IN A LIQUID SOLVENT IS SUBJECTED TOTHE ACTION OF AN ACID POLYMERIZATION CATALYST, THE IMPROVEMENT WHICHCOMPRISES DISSOLVING SAID NVINYL PYRROLE COMPOUND IN A SOLVENT SELECTEDFROM THE CLASS CONSISTING OF MONOCHLORO-, MONOBROMO, ANDMONOFLUORO-BENZENE AND ORTHO- AND META-DICHLORO-, DIBROMO- ANDDIFLUORO-BENZENE AND SUBJECTING THE THUS-OBTAINED SOLUTION, WHILE LIQUIDAND AT A TEMPERATURE BELOW 20* C., TO THE ACTION OF AN ACIDPOLYMERIZATION CATALYST IN SUCH A PREDETERMINED MINOR AMOUNT AS ISSUFFICIENT TO EFFECT COMPLETE POLYMERIZATION OF SAID N-VINYL PYRROLECOMPOUND, BUT WHICH IS LESS THAN THAT AT WHICH INSOLUBLE MATERIAL ISFORMED IN THE REACTION MASS.